Kotlin Professional Certificate case studies
Kotlin Professional Certificate · Put your knowledge to work in context.
The Kotlin Professional Certificate is a JetBrains credential aimed at developers who want to demonstrate practical Kotlin competence. According to the source material, JetBrains positions Kotlin within a broader ecosystem of tools, libraries, and integrations for building modern applications, and IntelliJ IDEA is described as the IDE for Java and Kotlin. The exam's published domains divide evenly across four areas: Kotlin language fundamentals and coding tasks; object-oriented and functional Kotlin programming; the standard library, collections, and coroutines; and tooling, testing, and IDE-based verification. That last domain reflects how JetBrains frames learning itself: the JetBrains Academy plugin lets learners work through coding tasks and custom verification tests inside JetBrains IDEs, with instant feedback and a focus on learning by doing. The Kotlin Professional Certificate case studies are 5 cases and about 3,547 words.
1The nullable lookup that passed CI
A payments team migrated a Java InventoryClient to Kotlin. The Java method signature is Map<String, Integer stockBySku() with no nullability annotations; the map values can be null for discontinued SKUs.
701 words, about 4 min2The deduplication job that kept 14% duplicates
A content team ingests 2.3M product tags nightly. Tag is declared as data class Tag(val name: String, val aliases: Array<String ) .
733 words, about 4 min3The shared flow that dropped every twelfth event
An Android analytics SDK exposes val events = MutableSharedFlow<Event (replay = 0) and a non-suspend fun track(event: Event) { if (!events.tryEmit(event)) logDropped() } . Three collectors attach at different times: the debug logger immediately, the uploader after a 200 ms initialization, and a screen observer only while visible.
720 words, about 4 min4Seven flaky tests in a 320-test suite
A Kotlin Multiplatform team has 320 JUnit 5 tests. Seven fail intermittently on CI (about 1 in 25 runs) but never locally.
644 words, about 3 min5The smart cast that vanished in a lambda
A Kotlin 2.0 service has private var activeSession: Session? A method does: if (activeSession != null && activeSession.isExpired()) { activeSession.refresh() } .
749 words, about 4 min